Fusel alcohols, also sometimes called fusel oils, or potato oil in Europe, are higher-order alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

s (that is, alcohols with more than two carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 atoms) formed by fermentation

Fermentation (biochemistry)

Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...

 and present in cider

Cider

Cider or cyder is a fermented alcoholic beverage made from apple juice. Cider varies in alcohol content from 2% abv to 8.5% abv or more in traditional English ciders. In some regions, such as Germany and America, cider may be termed "apple wine"...

, mead

Mead

Mead , also called honey wine, is an alcoholic beverage that is produced by fermenting a solution of honey and water. It may also be produced by fermenting a solution of water and honey with grain mash, which is strained immediately after fermentation...

, beer

Beer

Beer is the world's most widely consumed andprobably oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. It is produced by the brewing and fermentation of sugars, mainly derived from malted cereal grains, most commonly malted barley and malted wheat...

, wine

Wine

Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...

, and spirits

Distilled beverage

A distilled beverage, liquor, or spirit is an alcoholic beverage containing ethanol that is produced by distilling ethanol produced by means of fermenting grain, fruit, or vegetables...

 to varying degrees.

The term fusel is German

German language

German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....

 for "bad liquor".

Composition and taste

The compounds involved are chiefly:

• 1-propanol
• 2-propanol
  Isopropyl alcohol
  Isopropyl alcohol is a common name for a chemical compound with the molecular formula C3H8O. It is a colorless, flammable chemical compound with a strong odor...
  
  
• butanol (various isomers)
• amyl alcohol
  Amyl alcohol
  An amyl alcohol is any of 8 alcohols with the formula C5H11OH. A mixture of amyl alcohols can be obtained from fusel alcohol. Amyl alcohol is used as a solvent and in esterfication for example in the production of amyl acetate...
  
   (various isomers)
• furfural
  Furfural
  Furfural is an organic compound derived from a variety of agricultural byproducts, including corncobs, oat, wheat bran, and sawdust. The name furfural comes from the Latin word , meaning bran, referring to its usual source....
  
   (not an alcohol)

Excessive concentrations of these fractions may cause off flavours, sometimes described as "spicy", "hot", or "solvent-like". Some beverages, such as whisky

Whisky

Whisky or whiskey is a type of distilled alcoholic beverage made from fermented grain mash. Different grains are used for different varieties, including barley, malted barley, rye, malted rye, wheat, and corn...

, Siwucha, and traditional ale

Ale

Ale is a type of beer brewed from malted barley using a warm fermentation with a strain of brewers' yeast. The yeast will ferment the beer quickly, giving it a sweet, full bodied and fruity taste...

s and cider

Cider

Cider or cyder is a fermented alcoholic beverage made from apple juice. Cider varies in alcohol content from 2% abv to 8.5% abv or more in traditional English ciders. In some regions, such as Germany and America, cider may be termed "apple wine"...

s, are expected to have relatively high concentrations of fusel alcohols as part of the flavour profile. In other beverages, such as Korn

Korn (liquor)

Korn is a German colorless spirit that is usually made from fermented rye but may also be made from corn, barley, or wheat. Korn differs from vodka in that it is less rigorously filtered, which leaves more of the cereal taste in the finished spirit.Korn is the cheapest kind of spirit available in...

, vodka

Vodka

Vodka , is a distilled beverage. It is composed primarily of water and ethanol with traces of impurities and flavorings. Vodka is made by the distillation of fermented substances such as grains, potatoes, or sometimes fruits....

, and lager

Lager

Lager is a type of beer made from malted barley that is brewed and stored at low temperatures. There are many types of lager; pale lager is the most widely-consumed and commercially available style of beer in the world; Pilsner, Bock, Dortmunder Export and Märzen are all styles of lager...

s, the presence of fusel alcohols is considered a fault.

Formation and removal

Fusel alcohols are formed when fermentation

Fermentation (biochemistry)

Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...

 occurs:

• at higher temperatures
• at lower pH
• when yeast activity is limited by low nitrogen content

During distillation

Distillation

Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....

, fusel alcohols are concentrated in the "tails" at the end of the distillation run. They have an oily consistency, which is noticeable to the distiller, hence the other name "fusel oil". If desired, these heavier alcohols can be almost completely separated in a reflux still. Freeze distillation, on the other hand, does not remove fusel alcohols.

Health effects

There is a popular belief that fusel alcohol contributes to hangover symptoms. One study indicated that fusel alcohol has no more significant undesirable health effects (headache, nausea, etc.) than ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

, the primary active ingredient in all alcoholic beverages. This study involved an animal model of hangover, and its significance in humans is unclear.